Hi Denis,
> > ConnMan really should not care whether we are attached or
> not. Why do you need a trigger in ConnMan, anyway? As far as
> I can see, a GPRS connection should only be activated if some
> client of ConnMan requests it.
>
> Actually it should care. We do safe-guard against attaching while
> roaming...
I don't think so. Preventing GPRS attach and GPRS context activation during
roaming can be done based on network registation status. Besides, oFono
probably should be the component to enforce it, so that the feature cannot be
easily bypassed.
> Besides, ConnMan doesn't really work this way. Maybe in the
> future with
> the session API it would be able to, but not at the moment. I'll let
> Marcel explain this more if he wants too..
Admittedly, I haven't really looked at ConnMan. My assumption, though, is that
a PDP context is not activated by default when ConnMan starts up. I.e., someone
has to request the internet connectivity. Is that correct? Activating a context
by default would be very bad for power consumption and standby times, unless
both the handset and the network support CPC. The decision should be up to the
user.
> >> Besides, 24.008 cause codes give us plenty of hints of
> >> whether / when to
> >> re-attach, and only a few of them require 'special' handling.
> >>
> >> I still think that we should come up with some strategy to
> re-attach
> >> automatically when detached by the network.
> >
> > Even if you can come up with an algorithm, testing it is
> very very challenging. There are plenty of differences in
> operator networks and it is very difficult to cover all
> cases. Making sure that the algorithm works requires
> extensive IOT and Field testing. We really don't want a case,
> where oFono fails to re-attach for whatever reason. We also
> don't want the case where oFono has not yet attempted to
> re-attach (e.g. on a timer) and a PDP context activation
> fails, even though GPRS would actually be available.
> >
> > For the above reasons, retrying attach on PDP context
> activation makes sense as a safe-guard, regardless of whether
> we have a re-attach algorithm or not. We use on-demand attach
> in pretty much all our products (except for certain operator
> specific variants) precisely because it is certain to work.
> No funny business. If there is GPRS service, you get a
> connection. It is also an approach that should work with any
> AT modem as well.
> >
>
> You might be right, but I'd really like to see whether the re-attach
> algorithm would be good enough first...
But what re-attach algorithm? I sure don't have one up my sleeve...
As I said, extensive IOT and field testing (with mobility) is necessary in
order to see how the prospective algorithm works in practise. Even then, you
can't possibly cover all the angles. In practise, you end up discovering the
rest of the glitches when the first products are already out there. That is a
very expensive road indeed for a feature that is a bit dubious to begin with.
Why are we attaching to GPRS by default, anyway?
That said, various operators tend to have different requirements on this. Some
want autoattach, some want on-demand attach, and some want a UI for changing
the mode. In practise we will probably need at least a variation point on this
and possibly a setting to change the behaviour. I'd propose starting by adding
the on-demand attach code, to make sure that GPRS at least works in all cases.
MikaL
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